Laser activated magnetic field manipulation of laser driven ion beams

Abstract

A system for generating pulses of charged particles, comprising a high intensity pulsed laser emitting laser pulses which, when impacting a target, generate pulses of charged particles. The particles passes through an electromagnet energized by a low inductance current feed incorporating a light activated switch to turn the energizing current on and off. Part of the light of the laser pulse is directed onto the light activated switch, such that the magnetic field is optically synchronized with the generated pulses of charged particles. This enables energizing the magnet only during passage of the pulses, such that it is lighter and more energy efficient than prior art systems using CW electromagnets. Synchronization also enables selection of charged particles having a predetermined range of particle energy, by timing activation of the magnetic field such that it diverts onto a selected beam path only the particles having the predetermined range of energies.

The invention claimed is: 
     
       1. A method of generating pulses of charged particles, comprising:
 projecting laser pulses onto a target adapted to generate said pulses of charged particles when impacted by said laser pulses; 
 generating a pulsed magnetic field by means of an electromagnet energized by a current, said electromagnet being positioned to direct at least part of at least one pulse of said charged particles; 
 switching said current by means of a light activated switch; and 
 illuminating said light activated switch with light obtained from said laser pulses, such that said pulsed magnetic field is actuated in synchronization with generation of said pulses of charged particles. 
 
     
     
       2. A method according to  claim 1 , wherein said directing of said at least part of at least one pulse of charged particles comprises any one of scanning, diverting or focusing a beam of said charged particles. 
     
     
       3. A method according to  claim 1 , wherein said pulsed magnetic field is activated to direct the whole of said at least one pulse of said charged particles. 
     
     
       4. A method according to  claim 1 , wherein said pulsed magnetic field is activated to direct said at least one part of said at least one pulse of said charged particles. 
     
     
       5. A method according to  claim 4 , wherein said at least one part of said at least one pulse of said charged particles is a part having said preselected range of particle energy. 
     
     
       6. The method of  claim 5 , wherein said at least one electromagnet is positioned at such a distance from said target that the energy dispersion of said particles in said at least one pulse is sufficient that said preselected range of particle energy can be resolved temporally by the response time of said at least one electromagnet and its current feed. 
     
     
       7. A method according to  claim 4 , wherein said pulsed magnetic field directs particles having said preselected range of particle energy away from other particles in said at least one pulse. 
     
     
       8. A method according to  claim 4 , wherein said pulsed magnetic field is activated during that portion of said at least one laser pulse predetermined such that said pulsed magnetic field diverts said part of said at least one pulse having said preselected range of particle energy. 
     
     
       9. The method of  claim 1 , wherein said light obtained from said laser pulses is passed through an optical delay element, so as to control the time at which said illumination is applied to said light activated switch. 
     
     
       10. A method of selecting charged particles having a predetermined energy range, from a pulse of charged particles generated by impact of a laser pulse a target, said method comprising:
 supplying current from an optically switched source to at least one electromagnet generating a magnetic field disposed such that when activated, said charged particles are diverted from their original path; and 
 switching said at least one magnetic field in synchronization with said laser pulse for a predetermined time period, such that that part of said pulse of charged particles comprising particles of the energy range to be selected, is diverted by said at least one magnetic field. 
 
     
     
       11. A method according to  claim 10 , wherein said magnetic field is disposed at a distance from said target such that the energy dispersion of said particles in said at least one pulse is sufficient that particles of said energy range to be selected, can be resolved temporally. 
     
     
       12. A method according to  claim 10 , wherein said at least one magnetic field is activated from the beginning of said predetermined time period to the end of said predetermined time period. 
     
     
       13. A method according to  claim 10 , wherein said predetermined time period is selected by use of a variable optical delay line. 
     
     
       14. A system for selecting charged particles having a predetermined range of energies, from a pulse of charged particles having a range of energies, comprising:
 a first electromagnet and a second electromagnet in mutual proximity, such that when either of said electromagnets is activated, said charged particles are diverted from their original path; and 
 a control system adapted to activate said first electromagnet to produce a first magnetic field pulse commencing at the moment in time when it is desired that said first magnetic pulse field commence diversion of said pulse train of charged particles at one end of said predetermined range of energies, and to activate said second electromagnet to produce a second magnetic field pulse in the reverse direction at the moment in time when it is desired that said second magnetic pulse field terminate diversion of said charged particles at the other end of said predetermined range of energies. 
 
     
     
       15. The system of  claim 14  wherein said predetermined range of energies is delineated by the moments in time defined by the leading edges of said first and second magnetic field pulses. 
     
     
       16. The system of  claim 14  wherein said pulse of charged particles is generated by impact of a laser pulse on a target, said system further comprising optical control switches for switching currents producing said first and second magnetic field pulses. 
     
     
       17. A method of selecting charged particles having a predetermined range of energies, from a pulse of charged particles having a range of energies, comprising:
 providing a first magnetic field pulse and a second magnetic field pulse in mutual proximity, such that when either of said magnetic field pulses are applied to said pulse train of charged particles, said charged particles are diverted from their original path; and 
 applying said first magnetic field pulse to define the moment in time when it is desired that said first magnetic pulse field commence diversion of said pulse train of charged particles at one end of said predetermined range of energies, and applying said second magnetic field pulse in the reverse direction to define the moment in time when it is desired that said second magnetic pulse field terminate diversion of said charged particles at the other end of said predetermined range of energies. 
 
     
     
       18. The method of  claim 17  wherein said predetermined range of energies is delineated by the moments in time defined by the leading edges of said first and second magnetic field pulses. 
     
     
       19. The method of  claim 17  wherein said pulse train of charged particles is generated by impact of a laser pulse on a target, and said first and second magnetic field pulses are switched by optical control on currents activating said first and second magnetic field pulses.